The present invention relates to the field of marine seismic exploration. More particularly, the invention relates to an improved cable termination for securing cable ends used in marine seismic operations.
Marine seismic exploration is conducted to investigate the structure and character of subsurface geologic formations underlying a body of water. A seismic vessel tows one or more seismic sources and one or more seismic streamer cables through the water. The seismic sources typically comprise compressed air guns which generate a bubble pulse in the water. The energy from each bubble pulse propagates downwardly into the geologic formations and is reflected at the interfaces between subsurface geological formations and boundaries. The reflected energy is sensed with hydrophones attached to the seismic streamers.
Marine seismic surveys are often conducted with multiple streamers towed behind the seismic vessel. Up to twelve or more streamers can form an array behind the vessel and typically vary in length between three and twelve kilometers. Tail buoys are attached at the end of each streamer for carrying equipment such as radar reflectors, navigation equipment, and acoustic transponders. Hydrophones are attached to each streamer and are typically wired together in receiver groups spaced regularly along each streamer.
The deployment, operation, and retrieval of streamers requires handling and time. Each survey day is expensive and significantly increases survey costs. The streamers are transported to the survey site by the seismic vessel and are deployed into the water after the survey site has been reached. At the end of each survey line, the vessel turns around and charts the next pass. Vessel turns are complicated by the long streamers extending behind the vessel hull, and the towing radius is typically large to minimize the possibility of streamer fouling. When the survey is complete, the streamers are reeled onto the vessel deck for relocation to the next survey site. Deployment, use and retrieval of the streamers generates stress on the streamers and streamer cable connectors.
Cable connectors link individual streamer sections to form extended streamer cables. The cable connectors permit replacement of damaged streamer portions without requiring replacement of the entire streamer length. Marine seismic connectors have a low profile relative to the cable diameter to minimize drag and the corresponding acoustic "noise". The marine seismic connectors typically comprise a metal housing attached to the streamer cable ends and provide for electrical or optical connections for linking the data transmission paths between adjacent streamer sections. A plurality of discrete electrical or optical conductors for transmitting data, signals, and power are surrounded by a multi-strand armor sheath surrounding the conductors to protect such conductors against handling mishaps, shark attacks, contact with underwater obstructions, and other damage causes. The armor sheath also provides the function of providing structural strength to the streamer to prevent over stretching of the elastic streamer conductors.
Various efforts have been attempted to anchor the streamer and armor sheath to marine seismic streamer connectors. The streamer armor is typically attached to the streamer with epoxy adhesives. However, epoxy is relatively brittle and can crack due to fatigue failure. Following such failure, water can intrude within the cracks and damage the enclosed electrical connections. Additionally, epoxy does not effectively resist bending moments acting on the metal anchor strands at the seismic connector attachment. Such bending moments can flex the armor strands, thereby dislodging galvanization on the wire strand exteriors. If the galvanization defoliates from the metal strands, salt water can contact the bare metal strands and cause premature structural failure of the armor strength member.
Epoxy based connections are also limited by other factors. The materials forming epoxy compounds are classified as environmentally hazardous materials subject to reporting and handling restrictions. Additionally, the epoxy compound materials have a limited shelf life which limits the actual epoxy strength and can lead to failure of the epoxy material joint. This feature is particularly limiting for marine seismic operations sailing in remote locations months after the epoxy material is manufactured.
Marine seismic streamers present unique connection problems not found in conventional stranded electrical wires. Numerous cable connections have been developed for anchoring a seismic streamer to a cable termination end. U.S. Pat. No. 3,812,455 to Pearson (1974) disclosed mated seismic streamer couplers. U.S. Pat. No. 4,351,036 to Mollere (1982) disclosed a streamer cable connector link. U.S. Pat. No. 4,530,075 to Pearson (1985) and U.S. Pat. No. 4,526,430 to Williams (1985) each disclosed a seismic cable coupler having a sleeve for transmitting forces across the coupler. U.S. Pat. No. 4,500,980 to Copeland (1985) disclosed a connector assembly for anchoring streamer cables. U.S. Pat. No. 4,953,146 to McMurray (1990) disclosed a housing connected to a streamer. U.S. Pat. No. 4,879,719 to Dumestre (1989) and U.S. Pat. No. 5,214,612 to Olivier et al. (1993) disclosed latching mechanisms for connecting equipment to streamer cables. U.S. Pat. No. 5,513,151 to Morningstar et al (1996) disclosed a streamer coupler having tension member apertures having retaining members passing through the tension member eyes. U.S. Pat. No. 5,510,577 to Corrigan (1996) disclosed an electrical connector assembly having a deformable seal ring.
A need exists for an improved technology for anchoring marine cables such as streamers to connectors. The connection should be easy to implement, should be adjustable, and should withstand the large tensile forces and bending moments present in marine operations.